1. Field of the Invention
The present invention relates to a hand tool having a joint lock mechanism, especially a hand tool having a head of adjustable angles and allowing easier and more secure positioning. The present application claims priority based on ROC (Taiwan) Patent Application No. 093219593.
2. Description of the Related Art
U.S. Pat. No. 6,295,898, corresponding to TW421111, has disclosed an improved angle-adjustable wrench comprising a head and a handle. The head has a pivotal portion comprising a retaining area and an adjustment area disposed on the surface thereof and extending along the axis thereof. A stop member is disposed between the pivotal portion and a front side of the handle between two lugs thereof. The stop member has an engaging slot of an inverse U shape disposed at one side thereof and is adapted to cross over the front side of the handle between the two lugs and be moveable between the two lugs. A toothed portion is disposed on the other concave arced side thereof and is adapted to engage the retaining area of the head such that the stop member is moveable between the retaining area and the adjustment area so as to adjust and position the head to a certain angle more conveniently and securely.
However, U.S. Pat. No. 6,295,898 has the following defects: (1) the configuration of the retaining area and the adjustment area disposed at the pivotal portion of the head complicates processing “non-continuous” teeth of the convex portion; (2) the concave arced side of the stop member complicates processing teeth on the side and the precision is difficult to control; (3) in order to move the stop member to an “unlocked position” and ensure smooth pivoting between the head and the handle, a gap with a sufficient space between the stop member and the pivotal portion or the front side of the handle needs to be maintained, which in turn, results in adverse effects on the assembly of the wrench; (4) if the size of the gap is too small, the operation of adjusting will not be smooth when the stop member is moved from the “unlocked position” to a “locked position,”; (5) unless for other special designs, the engagement and positioning between a spring and a ball may be too loose when the stop member is moved to the “unlocked position”; (6) when the stop member is at the “locked position,” the locking of the head is obviously unstable and the engagement between the retaining area and the toothed portion of the stopping member may be “loose” due to an inappropriate external force because the head is merely slightly pushed by a spring.
Another design of a wrench disclosed in U.S. Pat. No. 6,745,650 comprises an inclined cambered surface disposed at a convex portion of a head. A buckle which is a block is disposed between the head and a handle. One end of the buckle with respect to the head is formed with a concave arced surface to engage the cambered surface of the convex portion of the head. However, since there is no tooth disposed on the cambered surface of the convex portion, the locking between the convex portion and the buckle is much less effective. It is also very difficult and inconvenient to process teeth on the cambered surface and the concave arced surface, and the precision is hard to control. In addition, when the buckle is moved to an “unlocked position,” a gap will be formed between the buckle and the convex portion, which has adverse effects on the assembly and operation of the wrench. Even if teeth were to be disposed on the cambered surface and the concave arced surface, the engagement between the buckle and the convex portion is not considered to be ideal and therefore is not easy to operate because the buckle is not pushed by any elastic force at the “unlocked position.”
From the above, it is necessary for the industry to provide a hand tool having an adjustable head with a joint lock mechanism, which offers convenient and secure angle adjustment and positioning and can overcome the defects mentioned in the prior art.